Human skin is composed of several layers, which include the dermis, epidermis, and stratum corneum. See MacKie, R. M., Clinical Dermatology (1996). The dermis has many elements, including vascular components which supply nutrients, fat cells which serve as energy depots and metabolic regulators, nerve cells, and elastic fibers. The epidermis lies exterior to the dermis and is composed of keratinocytes that produce growth factors important in the regulation of skin cell replication. The stratum corneum is the outermost barrier layer and is composed of cornified epidermal cells. The stratum corneum provides a barrier to loss of moisture and to environmental insults.
Skin is damaged by exposure to a variety of environmental factors, including ultraviolet light from sunlight or intentional tanning lights, and by tobacco smoke inhalation. Damage to skin is exacerbated by aging, and the combination effect is known as photoaging. Photoaging of skin results in thinning of the dermis, formation of the wrinkles, loss of skin elasticity, loss of natural oils, dryness, scaling, and irregular pigmentation. In the process of photoaging the collagen and elastin fibers of the dermis degrade and weaken, contributing to a thinning of the skin. In addition, microdeposits of fat are sometimes diminished in the skin. The muscle layers underlying the skin can also relax to contribute to a loose skin appearance. Conversely, some specific muscles associated with the skin can contract to cause frown lines, laugh lines, and other wrinkles or skin creases
The wide variety of treatments for photoaged skin and wrinkles may reflect, in part, the relative inefficacy of the treatments, the lack of control of the treatment by the individual, or the potentially adverse side effects of known treatments. Representative known skin treatments are discussed below.
A wide variety of chemical treatments have been used to resurface the skin Deep and mid-level treatments have used organic chemicals such as phenol or trichloroacetic acid. Undesirable after-effects from these treatments can include swelling, oozing, blistering, and pain More superficial chemical exfoliative treatments, or “peels,” include treatments with alpha hydroxy glycolic, lactic, or other acids, are used to remove skin layers, and have been used in combination with abrasive treatments. By thinning the stratum corneum, alpha hydroxy acids increase the sensitivity of the skin to sunlight. Some reports also suggest that they increase long term production of wrinkles. More fundamentally, such treatments render the patient more susceptible to the deleterious effects of ultraviolet radiation.
Topical treatment with retinoic acid (Retin A) is another common skin treatment and is widely used for acne treatment. Retinoic acid affects cell function and results in a loosening of the cells at the surface of the skin. Serious concerns exist, however, regarding whether retinoic acid treatment may play a role in the development of skin cancers. In an experimental model, topical application of retinoic acid augmented photocarcinogenesis by reducing the latency period, increasing the total numbers of tumors, and decreasing survival time. Halliday, G. M. et al., Topical retinoic acid enhances, and a dark tan protects, from subedemal solar-simulated photocarcinogenesis. 114 J. Invest. Dermatol. 923 (2000).
Abrasion techniques with wire brushes, diamond grinding wheels, microderm abrasion, or more recently, with laser ablation, are also used to smooth wrinkles and skin scars. Another abrasion method involves abrasion of the stratum corneum with aluminum oxide abrasives, e.g. Brasivol®. Marks, R. The effects of an abrasive agent on normal skin and on photoaged skin in comparison with topical tretinoin, 123 Br. J. Dermatol. 457 (1990). In this method, the desquamation (i.e. stripping) of the stratum corneum is increased. Moreover, several changes in the skin were noted: the epidermal labeling index, i.e., the replication of keratinocytes, was increased, the cutaneous blood flow was increased, the force necessary for skin extensibility was increased, and skin thickness was increased. However, increased desquamation is also associated with increased sensitivity to sunlight and thereby to photodamage of the skin, including wrinkling and dryness, and to an increased risk of neoplasia. Moreover, the method is reported to lead to minor dermatitis that can require use of hydrocortisone. U.S. Pat. No. 4,957,747
Abrasive skin cleaners are old in the art. The manufacture of Lava brand soap was begun in the nineteenth century. U.S. Pat. No. 5,910,476 to Kinsman, et al. discloses a soap bar having pumice or other abrasive. U.S. Pat. No. 5,441,666 to Dotolo discloses an abrasive hand cleaner having D-limonene and from about 2.5 to about 11 percent pumice by weight. U.S. Pat. No. 3,092,111 to Saperstein, et al. describes a composition and method using aluminum oxide for the therapeutic abrasion of human skin for the treatment of acne to induce desquamation.
Various treatments of aged skin have been proposed. The U.S. Pat. No. 4,957,747 to Stiefel describes a method for improvement of firmness and tone of aged skin by repeated desquamation using a suspension of fine aluminum oxide abrasive. The U.S. Pat. No. 5,720,963 to Smith discloses use of cerebrosides, which are biological regulators, to inhibit the repair of a disrupted skin moisture barrier.
Surgical techniques have also been used to improve skin appearance. Among these are facial reconstructions, including “face lifts,” which are used for more general aesthetic effects, and surgically remove the slack in loose, inelastic skin.
What has not been available is a way of stimulating renewal of the skin without topical biological regulators, desquamating abrasives, or exfoliating chemicals.